FBF-1 and FBF-2 are translational regulators maintaining germline stem cells in C. elegans (Crittenden et al., 2002). We previously reported that the localization and function of FBF-2 depends on the integrity of P granules, perinuclear RNA granules of germ cells (Strome and Wood, 1982; Pitt et al., 2000; Voronina et al., 2012). To understand the role of cofactors in FBF-2 function, we are characterizing FBF-2 interactome by mass-spectroscopy. To select the components of FBF-2 RNP contributing to FBF-2-mediated regulation, we employed a genetic interaction assay. We depleted candidate FBF-2-interacting partners by RNAi in N2 worms, as well as in
fbf-1(lf) mutant (Lamont et al., 2004), in which the worm relies solely on FBF-2 for stem cell maintenance, translational regulation, and fertility. Cofactors specific for FBF-2 should be required for FBF-dependent regulation in
fbf-1(lf) mutant, but not in a wild-type strain, where FBF-1 can compensate. The screen identified C. elegans homolog of La protein (provisionally named LHP-1) and dynein light chain DLC-1 as candidate FBF-2 cofactors. La protein contributes to multiple steps in RNA biogenesis in the nucleus, and has been recently implicated in the regulated translation of several mRNAs in the cytoplasm (Bayfield et al., 2012). DLC-1 is a cargo-binding component of dynein motor complex required for cell division (Gonczy et al., 1999), meiotic chromosomal synapsis (Sato et al., 2009), and regulation of meiotic entry (Dorsett and Schedl, 2009). Similar to
pgl-1(lf), both
lhp-1(RNAi) and
dlc-1(RNAi) in the
fbf-1(lf) background lead to derepression of FBF target reporter in the distal mitotic region and masculinization of germline; the phenotypes not observed after same RNAi treatments of the wild type or
fbf-2(lf) worms. Localization of FBF-2 to the nuclear periphery is maintained after
lhp-1(RNAi), but is lost after
dlc-1(RNAi), even when perinuclear P granules are normal. Our data is consistent with DLC-1 affecting FBF-2 subcellular distribution, and LHP-1 contributing to FBF-2 function downstream of its localization to P granules.